The present invention relates to a method of regulating a resistance value in a sensor circuit, and more particularly to the method of regulating the resistance value in the sensor circuit for enabling the resistance value in the sensor circuit provided with an electrostatic capacitance sensor or the like to be regulated easily.
Referring to FIGS. 3 to 5, a related method for regulating a resistance value in a sensor circuit of this type will be described. In FIG. 3, a switch device 1 includes a pair of first electrodes 3 mounted on a base plate 2, and a C-shaped second electrode 4 is circumferentially arranged around the first electrodes 3 so as to be outwardly apart therefrom. The first electrodes 3 and the second electrode 4 are covered with a resist 5, and a pair of carbon electrodes 6 are provided on an upper face of the resist 5 and above the first electrodes 3.
Moreover, there is provided a click rubber 7 above and opposed to the first electrodes 3 and the second electrode 4. The click rubber 7 has a substantially cylindrical body 8 and a flexible leg 9 extending downwardly from an outer peripheral part of the cylindrical body 8 at a lower end thereof. In addition, a conductive rubber 10 substantially in a disc-like shape is provided in a center part of the lower end of the cylindrical body 8. The conductive rubber 10, the first electrodes 3 and the second electrode 4 constitute an electrostatic capacitance sensor 13.
Further, a button 11 is mounted on an upper face of the click rubber 7. An upper cover 12 for covering an upper part of the click rubber 7, the first electrodes 3 and the second electrode 4, is provided to press down at a bottom part of the flexible leg 9 of the click rubber 7, so that an upper part of the button 11 projects through an opening 12a which is formed in an upper part of the upper cover 12.
FIG. 4 shows a sensor circuit 14 of the switch device 1. The sensor circuit 14 includes a resistor 16, for setting a resistance constant, which is connected to a line extending from a clock power source 15. The resistor 16 is composed of a high resistance element 17 having a relatively high resistance value and a pre-set variable resistor 18 capable of regulating the resistance value connected in series. The pre-set variable resistor 18 is connected to one of input terminals of an ENOR (Exclusive NOR) gate 19. Then, an end of the electrostatic capacitance sensor 13 is connected to the line between the pre-set variable resistor 18 and the ENOR gate 19. The electrostatic capacitance sensor 13 is composed of a capacitor 20 and a switch 21 connected in series, and the other end of the electrostatic capacitance sensor 13 is grounded.
On the other hand, a resistor 22 for setting a resistance constant is connected to another line extending from the clock power source 15. The resistor 22 is composed of a high resistance element 23 having a relatively high resistance value and a pre-set variable resistor 24 capable of regulating the resistance value connected in series. The pre-set variable resistor 24 is connected to the other input terminal of the ENOR gate 19.
In this state, the capacitor 20 corresponds to a circuit constituted by the conductive rubber 10, the first electrodes 3 and the second electrode 4, while the switch 21 corresponds to a circuit constituted by the conductive rubber 10 and the carbon electrodes 6.
Incidentally, when the button 11 is depressed, the flexible leg 9 of the click rubber 7 is flexed so that the conductive rubber 10 is brought into contact with the carbon electrodes 6 to establish electrical continuity between the carbon electrodes 6. As the button 11 is further pushed down, the conductive rubber 10 is pushed against the first electrodes 3 and the second electrode 4 which are covered with the resist 5. According to the pressure contact, electrostatic capacitance in the conductive rubber 10 is varied so that output from the conductive rubber 10 is thereby changed.
In other words, after the switch 21 has been turned on in the circuit 14, the output at the ENOR gate 19 is changed in accordance with the variation of the electrostatic capacitance of the capacitor 20.
FIG. 5 is a graph showing relationship between input pressure of the electrostatic capacitance sensor 13 provided by bringing the conductive rubber 10 into contact with the resist 5 and the output level thereof. As shown by a solid line, the output level rises substantially in proportion to an increase of the input pressure.
However, as shown by dotted lines in FIG. 5, there exists dispersion in the outputs of the respective electrostatic capacitance sensors 13 with respect to the input. The dispersion may incur instability of the output level of the electrostatic capacitance sensor 13 so that reliability as the electrostatic capacitance sensor 13 may be deteriorated.
Under the circumstances, the dispersion in the output levels has been adjusted by regulating the resistance values of the pre-set variable resistors 18 and 24. However, costs for components of the pre-set variable resistors 18 and 24 are relatively high, and regulation of the resistance values through the use of the pre-set variable resistors 18 and 24 takes a relatively long working time.
It is therefore an object of the present invention to provide a method and a structure for regulating a resistance value in a sensor circuit in which the resistance value in the sensor circuit can be easily regulated with a low cost.
In order to achieve the above object, according to the present invention, there is provided a method of regulating a resistance value in a pressure sensitive sensor circuit comprising the steps of:
providing a pressure sensitive sensor circuit including;
a first conductive path having a first resistor which has a first resistance value; and
a second conductive path having a second resistor which has a second resistance value lower than the first resistance value of the first resistor, and the second resistor connected to the first resistor in series; and
a third conductive path having an open circuit which is connected to the second resistor in parallel;
inspecting a relationship between input pressure and output level in the pressure sensitive sensor circuit; and
short-circuiting the open circuit of the third conductive path based on the result of the inspection.
In the above method, the second resistance value of the second resistor can be decreased by short-circuiting the open circuit of the third conductive path, so that the second resistance value in the pressure sensitive sensor circuit can be easily regulated with a low cost.
According to the present invention, there is also provided a sensor circuit comprising:
a first resistor having a first resistance value;
a second resistor having a second resistance value lower than the first resistance value of the first resistor, and connected to the first resistor in series; and
an adjuster for regulating a resistance value in the sensor circuit, including a pair of lands separated from each other for a solder joinable distance, and the pair of lands connected to the second resistor in parallel.
In the above structure, the second resistance value of the second resistor can be decreased by short-circuiting the pair of lands, so that the second resistance value in the sensor circuit can be easily regulated with a low cost.
Further, according to the present invention, there is also provided a sensor circuit comprising:
a first resistor having a first resistance value;
a second resistor having a second resistance value lower than the first resistance value of the first resistor, and connected to the first resistor in series; and
an adjuster for regulating a resistance value in the sensor circuit, including;
a first land, branched from upstream of the second resistor; and
a second land branched from downstream of the second resistor, and separated from the first land for a solder joinable distance.
In the above structure, the second resistance value of the second resistor can be decreased by short-circuiting between the first land and the second land, so that the second resistance value in the sensor circuit can be easily regulated with a low cost.
Further, according to the present invention, there is also provided a sensor circuit comprising:
a first resistor having a first resistance value;
second resistor having a second resistance value lower than the first resistance value of the first resistor, and connected to the first resistor in series; and
an adjuster for regulating a resistance value in the sensor circuit, including a closable switch which is connected to the second resistor in parallel.
In the above structure, the second resistance value of the second resistor can be decreased by short-circuiting the switch, so that the second resistance value in the sensor circuit can be easily regulated with a low cost.